Non-actinic fluorescent lamp



Dec. 18, 1956 BURNS 2,774,903

NON-ACTINIC FLUORESCENT LAMP Filed Jan. 1'7, 1951 A/VGS TROM U/V/TJ 30253/30 3340 3650 4000 7000 IIA IIIIIIIIIJ'IIII IN V EN TOR:

, 2,774,903 NON-ACTINIC FLUORESCENT LAMP Laurence Burns, Swampscott,Mass., assignor to Sylvania Electric Products Inc., Salem, Mass., acorporation of Massachusetts Application January 17, 1951, Serial No.206,440 10 Claims. (Cl. 313-109 This invention relates to electricdischarge lamps and particularly to fluorescent lamps.

An object of the invention is to reduce eye fatigue and the like fromfluorescent lamps by eliminating or reducing the amount of ultra-violetlight emitted by such lamps. A feature of the invention is a fluorescentlamp envelope which transmits visible but absorbs ultra-violet light andanother feature is a coating for this same purpose. Other objects,advantages and features of the invention Willbe apparent from thefollowing description taken in connection with the accompanying drawingin which:

Figure 1 is a representation of a spectrogram of an ordinary fluorescentlamp;

Figure 2 is a lamp according to the invention;

Figure 3 is a fixture according to the invention;

Figure 4 is another fixture according to the invention;

Figure 5 is a broken view in section, of a lamp according to amodification of the invention; 'and Figure 6 is a broken View, insection, of a lamp according to further modification of the invention.

It has been found that fluorescent lamps often produce eye fatiguegreater than that from incandescent lamps. This may be due to variousfactors, one of which is the ultraviolet emission from the lamps. Thelamps ordinarily produce the mercury spectrum, which includes radiation,or lines as in Figure l, at roughly 3650 Angstrom units, and also at3340, 3130 and 3025. These radiations cause the eye itself to fluoresce,and by thus reducing the sharpness of vision under the light, cause eyestrain. When the fluorescent materials used are a blend of magnesiumtungstate and zinc manganese beryllium silicate, there is very littleultraviolet radiation from the fluorescent powders themselves, but themercury radiations previous ly mentioned still are present. When calciumtungstate is used as one of the fluorescent materials, radiations justbelow, the blue are produced and when calcium silicate, activatedconjointly with maganese and lead is used, considerable radiation ofabout 3200 Angstrom units is produced. The latter phosphor produces abuif visible light but also some ultraviolet; it has two separatedemission bands.

Figure 2 shows a glass envelope 1, containing an inert gas, for example,argon at a few millimeters pressure, and mercury vapor, and having anelectrode 2, 3 sealed into each end. by the lead-in wires 4, 5, 6, 7. Afluorescent coating 8 is on the inside of the envelope 1. The envelope 1has heretofore been made of lead or lime glass which transmitsultraviolet in the region above 3000 Angstrom units to some extent,transmitting 3650 Angstroms very well.

According to my invention, the absorption of this glass for ultravioletmay be increased by use of additional iron, for example, ferrous oxide,in the glass or by use of an envelope of the glass now well-known asNoviol, made by the Corning Glass Works, of Corning, N. Y. Noviol O isgood.

If desired, the glass of the envelope 1 may remain unnited StatesPatent() ice changed, if an ultraviolet absorbing layer 14, 15 is usedon the inside or outside of the glass. A fluorescent material emittingVisible light in response to excitation by ultraviolet in the 3000 to3800 Angstrom range may constitute this layer 14, 15. This would be inaddition to the main fluorescent material which responds chiefly toradiations below 3000 Angstrom, such as the 2537 Angstrom mercuryradiation. Such a material would be zinc vanadate or uranium-activatedcalcium fluoride or sodium fluoride, for example. These give a yellow oryellowish-green light, and the main fluorescent matherials used wouldhave to be such, or so blended, as to give a white light, or the desiredcolor, in the presence of this additional light.

In some cases it may be more convenient to use an ultraviolet absorbingglass or plastic in the fixture, as shown schematically in cross-sectionin Figure 3, where the lamp 110 is surrounded by the reflector 11 andthe light transmitting, ultraviolet absorbing piece 12.

In other cases, it may be desirable to use the louvres 13 as shown inFigure 4. These will shield the eyes from the direct light from the lampor lamps 10 in the reflector 11, and may have a coating 18 of asubstance which reflects visible light but absorbs ultraviolet. Thefluorescent materials previously mentioned may be used for this purpose,being applied in a varnish, a lacquer, or a plastic. The louvres 13 maybe, for example, as shown in application, Serial No. 481,040, filedMarch 29, 1943, now Patent 2,364,992 by Rene G. Maurette. When a blendof fluorescent powders including calcium silicate activated with bothmanganese and lead conjointly is used, it may be desirable to mix inwith the blend a green or yellowish-green fluoresciug material,responsive to the ultraviolet emitted by the calcium silicate. This willeliminate or reduce the amount of ultraviolet emitted by the coating-aswell as that emitted by the mercury vaporand will at the same time addsome green light to that emitted by the calcium silicate. Since thespectrum of calcium silicate, even when supplemented by the spectrum ofmagnesium tungstate physically admixed with it, is generally slightlydeficient in the green, this serves a double purpose.

The uranium-activated calcium fluorides and other materials of U. S.Patent 2,323,284, issued June 29, 1943, to W. P. Toorks may prove usefulin this respect. Zinc vanadate may be useful if the yellow portion ofthe spectrum is to be enhanced.

The usual lead or lime glass used in fluorescent lamp bulbs decreasesrapidly in transmission with wavelength, as the latter is reduced below3300 Angstroms, so that the wavelengths above this value are the chiefones to be absorbed from the present lamps although some of the lowerwavelengths down to 3000 Angstroms are transmitted to a lesser extent.When the fluorescent material used has high emission below 3300Angstroms, considerable radiation below that wavelength may be emitteddespite the low glass transmission of regular bulbs at that wavelength.

Where an absorbing layer 14, 15 is used in the lamp, it should beordinarily placed between the regular fluorescent layer 8 and the glassenvelope 1, unless it is placed on theoutside of the glass envelope, orunless it has high transmission for the 2500 Angstrom radiation whichexcites the main fluorescent material. In addition to the absorbingmaterials previously mentioned, zinc or titanium oxides will be foundquite effective, zinc being especially effective against the 3650Angstrom wavelengths and lower. Zinc oxide will also be found good as amaterial for the coating 17, 18 on reflector 11 and louvres 13, inFigure 2, for it does not reflect ultraviolet light but does reflectvisible light. Titanium is also useful in this respect, but is not aseffective in preventing reflection as it is in preventing transmission.Lithopone is effective against transmission, but not against reflection.

Crookes glass, particularly that known as Crookes A, reduces the 3650radiation to a small percentage, and substantially eliminates thoselower, in a thickness of 2 millimeters. It is thus very effective as afilter glass 12 in the fixture of Figure 2, and is also eflective as theglass of the lamp envelope.

Where the glass transmission is reduced by addition of ferrous oxide tothe batch from which it is made, 0.2 to 1% will generally be foundsuflicient. Titanium and cerium oxides have also been found effectivefor this purpose.

In Figures 3 and 4, the filter 12 and louvres 13 are shown incross-section. They extend longitudinally with the tube 10.

A thin gold film on the glass envelope may sometimes be desirable as thefilter 14, 15 which transmits visible and absorbs ultraviolet light.Such a film has the additional advantage that it allows starting of thelamp at lower voltage and makes its starting independent of the ambienthumidity. In ordinary commercial fluorescent lamps as now sold, thenecessary starting voltage rises with humidity.

This rise may also be reduced in a different manner without the goldcoating, by providing spring metal pieces 16 electrically connected toand extending from the metal reflector 11 ordinarily used with the lamp10, and bearing on the glass envelope 1 of the lamp 10 near the cathode3. One may be used at each end of the lamp, but if the reflector 11 is,directly or indirectly, grounded to one end of the lamp, the springpiece bearing on the glass may be used at only the ungrounded end of thelamp 10. The spring piece 16 will ordinarily bear on the side of thelamp 10 nearest the reflector 11, to be out of sight and to facilitateinsertion of the lamps in its sockets. This spring piece 16 may, ofcourse, be used with the present commercial fluorescent lamps, which donot have ultraviolet absorbing means. And conversely, such a springpiece 16 is not at all necessary with my ultraviolet absorbing lampsunless a better starting condition is desired than is usual in presentcommercial lamps.

This application is in part a continuation of my copending applicationsSerial No. 568,737, filed December 18, 1944, now Patent 2,452,518 andSerial No. 50,608 filed September 22, 1948, now abandoned.

What I claim is:

l. A fluorescent lamp having air internal fluorescent coating andelectric discharge emitting long-wavelength ultraviolet radiations andvisible radiations and an outer envelope of ultraviolet-absorbinglight-transmitting glass containing a substance which aborbs longwavelength ultraviolet radiations and selected from the group consistingof: zinc oxide, titanium oxide, cerium oxide, said glass being selectedfrom the group consisting of lead glass and lime glass.

2. A fluorescent lamp having an internal electric discharge andfluorescent coating emitting long-wavelength ultraviolet radiations andvisible radiations and an outer envelope of ultra-violet-absorbing lighttransmitting glass containing zinc oxide to absorb long wavelengthultraviolet radiations, said glass being selected from the groupconsisting of lead glass and lime glass.

3. A fluorescent lamp having an internal electric discharge andfluorescent coating emitting long-wavelength ultraviolet radiations andvisible radiations and an outer envelope of ultra-violet-absorbing lighttransmitting glass containing titanium oxide to absorb long wavelengthultraviolet radiations, said glass being selected from the groupconsisting of lead glass and lime glass.

4. A fluorescent lamp having an internal electric discharge andfluorescent coating emitting long-wavelength ultraviolet radiations andvisible radiations and an outer envelope of ultra-violet-absorbing lighttransmitting glass containing cerium oxide to absorb long wavelengthultraviolet radiations, said glass being selected from the groupconsisting of lead glass and lime glass.

5. A fluorescent lamp having an internal fluorescent coating emittingultraviolet and visible radiation and an envelope of light-transmittingglass containing on its inner surface a coating between the glass andthe fluorescent coating, said second-mentioned coating comprising asubstance selected from the group consisting of zinc oxide, titaniumoxide, cerium oxide.

6. A fluorescent lamp having an internal fluorescent coating emittingultraviolet and visible radiation and an envelope of light-transmittingglass containing on its inner surface a coating of titanium oxidebetween the glass and the fluorescent coating.

7. A fluorescent lamp having an internal fluorescent coating emittingultraviolet and visible radiation and an envelope of light-transmittingglass containing on its inner surface a coating of zinc oxide betweenthe glass and the fluorescent coating.

8. A fluorescent lamp comprising: a sealed glass envelope; a coating onthe inside of said envelope and comprising a substance selected from thegroup consisting of zinc oxide, titanium oxide, cerium oxide; and afluorescent coating over said oxide coating on the inside of said bulb.

9. A fluorescent lamp comprising: a sealed glass envelope; a coating oftitanium oxide on the inside surface of said envelope; and a fluorescentcoating over said oxide coating on the inside of said bulb.

10. A fluorescent lamp comprising: a sealed glass envelope; a coating ofzinc oxide on the inside surface of said envelope; and a fluorescentcoating over said oxide coating on the inside of said bulb.

References Cited in the file of this patent UNITED STATES PATENTS1,536,919 Parkinson May 5, 1925 1,634,182 Gell June 28, 1927 2,244,558Krautz June 3, 1941 2,282,601 Blau May 12, 1942 2,314,096 Leverenz Mar.16, 1943 2,359,789 Pincus Oct. 10, 1944 2,393,469 Hooley Jan. 22, 19462,405,261 Levi et al. Aug. 6, 1946 2,413,940 Bickford Jan. 7, 19472,436,847 Wolfson Mar. 2, 1948 2,450,548 Gisolf Oct. 5, 1948 2,476,681Overbeek July 19, 1949 2,582,453 Pincus Jan. 15, 1952 OTHER REFERENCESMultilayer Films of High Reflecting Power, by C. H. Cartwright and A. F.Turner, Physical Review, vol. 55, page 1128, June 1, 1939.

